Meiotic homolog pairing and attachment are essential for normal chromosome segregation during meiosis I. It is thought that both meiotic recombination and sister chromatid cohesion are required for homolog attachment at late prophase I and metaphase I. Sister chromatid cohesion is removed from the chromosomal arms at the metaphase I/anaphase I transition, allowing homologs to separate. Arabidopsis is an excellent system to investigate the molecular control of meiosis because its available molecular genetic tools and the feasibility of good cytological studies. An Arabidopsis mutant, sds, was isolated and found to be defective in maintaining meiotic homolog attachment at prophase I. The SDS gene encodes a novel cyclin-like protein, suggesting that a cyclin-CDK complex is required for homolog attachment. In addition, it was shown that another Arabidopsis gene, ASK1, is required for release of homolog for separation at anaphase I, and that the ask1 mutant meiotic cells show persistent localization of the putative Arabidopsis meiotic cohesion SYN1 on chromosomes at late metaphase I and anaphase I. Preliminary evidence suggests that SDS may genetically interact with ASK1, supporting the hypothesis that SDS may also regulate the removal of cohesions from the chromosome. It is also possible that SDS may regulate meiotic recombination. These Arabidopsis mutant and genes will be used to gain new insights about the control of meiotic homolog attachment, using genetic, cytological and molecular approaches. Both cytological and genetic experiments will be carried out to test these hypotheses about SDS function. In addition, genetic interaction between SDS and SYN1and ASK1 will be investigated. Because SDS is a putative novel cyclin, additional experiments will be performed to test for interactions between SDS and CDKs, to probe for possible functions of CDKs in meiosis, and to identify and characterize genes what encode proteins that interact with SDS. Furthermore, molecular and cell biological experiments will be done to characterize the expression pattern and protein localization of SDS, and to isolate a putative SDS-like gene.